This invention relates to radial ply pneumatic tires which are used on passenger, truck, off-the-road, tractor and industrial vehicles, but particularly to truck tires. It specifically relates to such tires in which the reinforcing cords in the body plies are radially directed and consist of an inextensible material, such as glass, steel wire and Kevlar. The normal, commercial tire employing this type of construction, whether it be truck or passenger, has the end of the reinforcing body ply wrapped around the bead bundle either by turning the ply end up or down around the bead bundle. In the usual construction, the tire may also have a bead wrap around the bead bundle. The cords in the bead wrap usually form an angle to the radial plane of the tire.
In the prior art constructions of this type of tire, the manufacturing costs and problems have been extreme. Due to the inherent stiffness in the inextensible reinforcing cords of the body ply, it is difficult and costly to wrap the ply ends around the bead bundle. It is also difficult and costly to wrap the bead wrap around the bead bundle when it contains stiff, inextensible cords that form an angle to the radial direction of the tire. These problems often result in a tire failure in the bead area due to a separation at either the turned up edge of the body reinforcing ply or at the edges of the bead wrap.
The prior art constructions contain a bead reinforce ply having inextensible cords at a bias to the radial plane of the tire to strengthen and stiffen the tire bead area. The presence of this ply causes construction problems and resulting failures by separation at the edges of these reinforce plies. In this invention these bias reinforce plies may be eliminated.
The present invention departs from the prior art in several aspects, one of which is the elimination of the necessity to wrap the end of the reinforcing body ply around the bead bundle. The concept of no turn ups of the ends of the body ply has been taught, see, for example, U.S. Pat. Nos. 1,219,420; 1,393,952; 3,062,259 and 3,386,486; French Pat. Nos. 1,124,766 and 1,127,521 and British Pat. No. 990,524.
The patents listed above disclose (1) the elimination of wrapping the ends of body fabrics around the bead bundle, (2) the cord angle of such body plies may be radial or biased, (3) the cords in the body plies may be an inextensible or extensible material, (4) the cords of the bead wrap may be an extensible or inextensible material that are parallel to or form angles to the radial direction of the tire, and (5) the body ply may be sandwiched between the ends of the bead wrap.
Some of the prior art referred to above, specifically British Pat. No. 990,524, discloses a radial ply body and a radial ply bead wrap. However, in this type of prior art the body ply is made of an extensible cord, rayon, and the bead wrap is made of an inextensible cord, steel. The inherent differences in the properties of the cords in these two plies, specifically modulus, result in the cords not acting together as if they were one ply, as does the present invention.
Also, in the prior art the body ply ends are sandwiched between the ends of the bead wrap. This means that the bead wrap may not be assembled onto the bead bundle prior to the application of the bead bundle on the tire building drum but that the bead wrap must first be placed on the building drum, then the bead bundle, then the body ply and then the free end of the bead wrap turned up to engulf the bead bundle and the body ply end. This prior art construction obviously does not eliminate the need for the expensive turn up operation in the tire building operation as does the present invention.
It is an object of this invention to provide a bead construction for a radial ply tire which is economic to manufacture, strong and performs satisfactorily.